Grazing-incidence Small-angle X-ray Scattering Patterns Research Articles

Strategy to simulate and fit 2D grazing-incidence small-angle X-ray scattering patterns of nanostructured thin films.

Grazing-incidence small-angle X-ray scattering (GISAXS) is a widely used method for the characterization of the nanostructure of supported thin films and enables time-resolved in situ measurements. The 2D scattering patterns contain detailed information about the nanostructures within the film and at its surface. However, this information is distorted not only by the reflection of the X-ray beam at the substrate-film interface and its refraction at the film surface but also by scattering of the substrate, the sample holder and other types of parasitic background scattering. In this work, a new, efficient strategy to simulate and fit 2D GISAXS patterns that explicitly includes these effects is introduced and demonstrated for (i) a model case nanostructured thin film on a substrate and (ii) experimental data from a microphase-separated block copolymer thin film. To make the protocol efficient, characteristic linecuts through the 2D GISAXS patterns, where the different contributions dominate, are analysed. The contributions of the substrate and the parasitic background scattering - which ideally are measured separately - are determined first and are used in the analysis of the 2D GISAXS patterns of the nanostructured, supported film. The nanostructures at the film surface and within the film are added step by step to the real-space model of the simulation, and their structural parameters are determined by minimizing the difference between simulated and experimental scattering patterns in the selected linecuts. Although in the present work the strategy is adapted for and tested with BornAgain, it can be easily used with other types of simulation software. The strategy is also applicable to grazing-incidence small-angle neutron scattering.

Highly oriented NiSi2@Si thin-nanocomposite produced by solid state diffusion: Morphological and crystallographic characterization

This article describes a morphological and crystallographic multi-technique characterization of a 2D-nanocomposite consisting of highly oriented NiSi2 nanoplates endotaxially grown inside a single-crystalline Si(001) wafer close to its external surface. This nanostructured material is prepared using a novel procedure which promotes the diffusion of Ni atoms from a deposited Ni-dopped-SiO2 thin film into the volume of a Si(001) flat wafer under controlled thermodynamic conditions. High Resolution Scanning Transmission Electron Microscopy images reveal the formations of well oriented thin hexagonal nanoplates totally buried inside a Si(001) wafer and randomly oriented nearly spherical Ni nanocrystals located inside the Ni-doped SiO2 thin film and also inside a thin layer close to external surface of the Si(001) wafer. The NiSi2 nanoplates formed by endotaxial growth have their large hexagonal flat surfaces parallel to one of the four Si{111} crystallographic planes and exhibit coherent 7A-type interfaces with the host Si matrix. Additional analyses of Grazing-Incidence Small-Angle X-ray Scattering patterns - which probe a high number of nanoparticles - indicated that the average thickness and maximum diameter of NiSi2 nanoplates are 12 nm and 118 nm, respectively, and the average radius of Ni nanocrystals is 1.7 nm. The described process for obtaining 2D-NiSi2@Si nanocomposites opens new possibilities for exploiting the structural features of these materials for use in devices requiring anisotropic electrical transport properties.

Designing Anion-Exchange Ionomers with Oriented Nanoscale Phase Separation at a Silver Interface

Performance of polymer electrolyte-based energy systems is significantly impacted by transport within the electrode catalyst layer, where ionomer thin films coat catalyst particles. Proton exchange ionomer thin films have been thoroughly characterized, but few studies have critically examined anion-exchange ionomer (AEI) thin films. Further, none have reported nanoscale phase separation for hydrocarbon AEIs, which is critical to mitigate transport resistances. In this work, a set of hydrocarbon-based AEIs with nanoscale phase separation are developed from tunable block copolymer systems composed of polyisoprene (PIp) and polychloromethylstyrene (PCMS). The effect of the PIp/PCMS ratio, architecture, and thickness on the thin-film morphology of the neutral block copolymer precursors on silicon and silver substrates is investigated using grazing-incidence small-angle X-ray scattering (GISAXS) and atomic force microscopy (AFM). AEIs are prepared by quaternizing with trimethylamine or methylpiperidine and their cation-dependent morphology is characterized at 60 °C and 95% RH. A perpendicularly aligned morphology is observed on silver, while no phase separation is observed on silicon, indicating that silver–polymer interfacial interactions drive phase separation. After quaternization, dipole–dipole interactions induce some disorder, but nanoscale phase separation is still maintained. GISAXS patterns are modeled using a Unified Fit approach to understand water uptake and swelling, and recommendations for AEI design are presented.

Carbon Deposition on Hematite (α-Fe2O3) Nanocubes by Annealing in the Air: Morphology Study with Grazing Incidence Small Angle X-ray Scattering (GISAXS)

GISAXS has been used to study morphology change of α-Fe2O3 nanocubes after annealing processes. A submonolayer of the nanocubes was deposited on a Si(100) substrate. While an annealing at 400 °C in vacuum does not change a GISAXS pattern from as-prepared nanocubes submonolayer, subsequent annealing in air at the same temperature altered the GISAXS pattern significantly. SEM images showed that the air-annealed nanocubes were coated with thin layers which were identified as amorphous carbon layers based on Raman measurements. GISAXS simulations from morphologies of nanocube with 38 nm side-length and core-shell (nanocube-core and 7 nm thick carbon-shell) reproduced measured patterns from the vacuum- and the air-annealed nanocubes, respectively. The current study provides new approach for in-situ characterization of carbon deposition on a uniform shape nanoparticle through monitoring of deposited carbon thickness.

Novel theoretical approach to the GISAXS issue: the Green function formalism using the q-Eigenwaves propagating through a twofold rough-surfaced medium

To describe the 1D and 2D patterns of the grazing-incidence small-angle X-ray scattering (GISAXS) from a rough fractal surface, the novel integral equations for the amplitudes of reflected and transmitted waves are derived. To be specific, the analytical expression for the 2D total intensity distribution frac{{dR_{tot} left( {theta ,phi ;theta_{0} } right)}}{dOmega } is obtained. The latter represents by itself a superposition of terms related to the GISAXS specular frac{{dR_{spec} left( {theta ;theta_{0} } right)}}{dOmega } and diffuse frac{{dR_{dif} left( {theta ,phi ;theta_{0} } right)}}{dOmega } patterns, respectively. Hereafter, theta is the scattering meridian angle, phi is the scattering azimuth angle; theta_{0} is the angle of incidence. By using the above analytical expressions, the 1D and 2D GISAXS patterns are numerically calculated. Some new experimental measurements of the specular reflectivity curves Rspec(theta_{0}) related to the fused quartz and crystal Si(111) samples have been carried out. Based on the theoretical approach developed, a direct least-squared procedure in a χ2-fit fashion has been used to determine the corresponding values of the root-mean-square roughness σ from the specular GISAXS reflectivity data.

Classification of grazing-incidence small-angle X-ray scattering patterns by convolutional neural network.

Grazing-incidence small-angle X-ray scattering (GISAXS) patterns have multiple superimposed contributions from the shape of the nanoscale structure, the coupling between the particles, the partial pair correlation, and the layer geometry. Therefore, it is not easy to identify the model manually from the huge amounts of combinations. The convolutional neural network (CNN), which is one of the artificial neural networks, can find regularities to classify patterns from large amounts of combinations. CNN was applied to classify GISAXS patterns, focusing on the shape of the nanoparticles. The network found regularities from the GISAXS patterns and showed a success rate of about 90% for the classification. This method can efficiently classify a large amount of experimental GISAXS patterns according to a set of model shapes and their combinations.

Dynamic Organization of Ligand-Grafted Nanoparticles during Adsorption and Surface Compression at Fluid-Fluid Interfaces.

Monolayers of ligand-grafted nanoparticles at fluid interfaces exhibit a complex response to deformation due to an interplay of particle rearrangements within the monolayer, and molecular rearrangements of the ligand brush on the surface of the particles. We use grazing-incidence small-angle X-ray scattering (GISAXS) combined with pendant drop tensiometry to probe in situ the dynamic organization of ligand-grafted nanoparticles upon adsorption at a fluid–fluid interface, and during monolayer compression. Through the simultaneous measurements of interparticle distance, obtained from GISAXS, and of surface pressure, obtained from pendant drop tensiometry, we link the interfacial stress to the monolayer microstructure. The results indicate that, during adsorption, the nanoparticles form rafts that grow while the interparticle distance remains constant. For small-amplitude, slow compression of the monolayer, the evolution of the interparticle distance bears a signature of ligand rearrangements leading to a local decrease in thickness of the ligand brush. For large-amplitude compression, the surface pressure is found to be strongly dependent on the rate of compression. Two-dimensional Brownian dynamics simulations show that the rate-dependent features are not due to jamming of the monolayer, and suggest that they may be due to out-of-plane reorganization of the particles (for instance expulsion or buckling). The corresponding GISAXS patterns are also consistent with out-of-plane reorganization of the nanoparticles.

Reconstructing detailed line profiles of lamellar gratings from GISAXS patterns with a Maxwell solver

Laterally periodic nanostructures have been investigated with grazing-incidence small-angle X-ray scattering (GISAXS) by using the diffraction patterns to reconstruct the surface shape. To model visible light scattering, rigorous calculations of the near and far field by numerical solution of Maxwell's equations with a finite-element method are well established. The application of this technique to X-rays is still challenging, owing to the discrepancy between the incident wavelength and the finite-element size. This drawback vanishes for GISAXS because of the small angles of incidence, the conical scattering geometry and the periodicity of the surface structures, which allows a rigorous computation of the diffraction efficiencies with sufficient numerical precision. To develop metrology tools based on GISAXS, lamellar gratings with line widths down to 55 nm were produced by state-of-the-art electron-beam lithography and then etched into silicon. The high surface sensitivity of GISAXS in conjunction with a Maxwell solver allows the detailed reconstruction of the grating line shape for thick non-homogeneous substrates as well. The reconstructed geometric line-shape models are statistically validated by applying a Markov chain Monte Carlo sampling technique which reveals that GISAXS is able to reconstruct critical parameters like the widths of the lines with sub-nanometre uncertainty.

In situ grazing-incidence small-angle X-ray scattering observation of block-copolymer templated formation of magnetic nanodot arrays and their magnetic properties

The fabrication of bit-patterned media (BPM) is crucial for new types of hard disk drives. The development of methods for the production of BPM is progressing rapidly. Conventional lithography reaches the limit regarding lateral resolution, and new routes are needed. In this study, we mainly focus on the dependence of the size and shape of magnetic nanodots on the Ar+-ion etching duration, using silica dots as masks. Two-dimensional (2D) arrays of magnetic nanostructures are created using silica-filled diblock-copolymer micelles as templates. After the self-assembly of the micelles into 2D hexagonal arrays, the polymer shell is removed, and the SiO2 cores are utilized to transform the morphology into a (Co/Pt)2-multilayer via ion etching under normal incidence. The number of preparation steps is kept as low as possible to simplify the formation of the nanostructure arrays. High-resolution in situ grazing-incidence small-angle X-ray scattering (GISAXS) investigations are performed during the Ar+-ion etching to monitor and control the fabrication process. The in situ investigation provides information on how the etching conditions can be improved for further ex situ experiments. The GISAXS patterns are compared with simulations. We observe that the dots change in shape from cylindrical to conical during the etching process. The magnetic behavior is studied by utilizing the magneto-optic Kerr effect. The Co/Pt dots exhibit different magnetic behaviors depending on their size, interparticle distance, and etching time. They show ferromagnetism with an easy axis of magnetization perpendicular to the film. A systematic dependence of the coercivity on the dot size is observed.

Lamellar body mimetic system: An up-to-down repairing strategy of the stratum corneum lipid structure

Epidermal lamellar bodies (LBs) are organelles that secrete their content, mainly lipids and enzymes, into the intercorneocyte space of the stratum corneum (SC) to form the lamellar structure of this tissue. Thus, LBs have a key role in permeability and the microbial cutaneous barrier. In this work, a complex lipid system that mimics the morphology, structure and composition of LBs has been designed. To evaluate the effect of this system on delipidized SC, in vitro experiments using porcine skin were performed. The microstructure of SC samples (native, delipidized and, delipidized after treatment) was evaluated by freeze substitution transmission electron microscopy (FSTEM) and grazing-incidence small-angle X-ray scattering (GISAXS). Delipidized SC samples showed no evidence of lipid lamellae after extraction with organic solvents. However, after treatment with the LB mimetic system, new lamellar structures between corneocytes were detected by FSTEM, and high intensity peaks and reflections were found in the GISAXS pattern. These results demonstrate a strong effect of the treatment in repairing part of the lipid lamellar structure of the SC. Accordingly, future research could extend the use of this system to repair skin barrier dysfunction.

Probing the surface microstructure of layer-by-layer self-assembly chitosan/poly(l-glutamic acid) multilayers: A grazing-incidence small-angle X-ray scattering study.

This study characterized the surface structure of layer-by-layer self-assembly chitosan/poly(L-glutamic acid) multilayers through grazing-incidence small-angle X-ray scattering (GISAXS), X-ray reflectivity (XRR), and atomic force microscopy (AFM). A weakly long-period ordered structure along the in-plane direction was firstly observed in the polyelectrolyte multilayer by the GISAXS technique. This structure can be attributed to the specific domains on the film surface. In the domain, nanodroplets that were formed by polyelectrolyte molecules were orderly arranged along the free surface of the films. This ordered structure gradually disappeared with the increasing bilayer number because of the complex merging behavior of nanodroplets into large islands. Furthermore, resonant diffuse scattering became evident in the GISAXS patterns as the number of bilayers in the polyelectrolyte multilayer was increased. Notably, the lateral cutoff length of resonant diffuse scattering for these polyelectrolyte films was comparable with the long-period value of the ordered nanodroplets in the polyelectrolyte multilayer. Therefore, the nanodroplets could be considered as a basic transmission unit for structure propagation from the inner interface to the film surface. It suggests that the surface structure with length scale larger than the size of nanodroplets was partially complicated from the interface structure near the substrate, but surface structure smaller than the cutoff length was mainly depended on the conformation of nanodroplets.

In situ monitoring of laser-induced periodic surface structures formation on polymer films by grazing incidence small-angle X-ray scattering.

The formation of laser-induced periodic surface structures (LIPSS) on model spin-coated polymer films has been followed in situ by grazing incidence small-angle X-ray scattering (GISAXS) using synchrotron radiation. The samples were irradiated at different repetition rates ranging from 1 up to 10 Hz by using the fourth harmonic of a Nd:YAG laser (266 nm) with pulses of 8 ns. Simultaneously, GISAXS patterns were acquired during laser irradiation. The variation of both the GISAXS signal with the number of pulses and the LIPSS period with laser irradiation time is revealing key kinetic aspects of the nanostructure formation process. By considering LIPSS as one-dimensional paracrystalline lattice and using a correlation found between the paracrystalline disorder parameter, g, and the number of reflections observed in the GISAXS patterns, the variation of the structural order of LIPSS can be assessed. The role of the laser repetition rate in the nanostructure formation has been clarified. For high pulse repetition rates (i.e., 10 Hz), LIPSS evolve in time to reach the expected period matching the wavelength of the irradiating laser. For lower pulse repetition rates LIPSS formation is less effective, and the period of the ripples never reaches the wavelength value. Results support and provide information on the existence of a feedback mechanism for LIPSS formation in polymer films.

Growth temperature effect on the structure of CoPt islands on NaCl(001) studied by grazing-incidence small-angle X-ray scattering

The structure (size, shape, orientation) of CoPt alloy islands formed on NaCl(001) substrates was investigated using grazing-incidence small-angle X-ray scattering (GISAXS) combined with electron and X-ray diffraction and transmission electron microscopy. Co50Pt50and Co25Pt75islands formed at 473 K by co-deposition of Co and Pt species are oriented along the [001] direction, and their shapes are well described as truncated spheres with lateral sizes of around 4–5 nm. In contrast, using the same Co and Pt atomic fluxes, co-deposition at 673 K leads to the formation of strongly enriched Pt islands with larger sizes, and different orientations and shapes. The Pt enrichment is attributed to a large increase in the difference between the Co and Pt condensation coefficients with deposition temperature. Surprisingly, for the island assemblies formed at 673 K, the GISAXS patterns are dominated by the scattered intensities of the [001]-oriented islands with a truncated octahedron shape, thus masking the contributions of the [111]- and [110]-oriented islands which can exhibit larger sizes.

Erratum: Quantitative analysis of nanoripple and nanoparticle patterns by grazing incidence small-angle x-ray scattering 3D mapping [Phys. Rev. B85, 235415 (2012)

After publication of this article, we discovered that the two-dimensional (2D) experimental grazing incidence small-angle x-ray scattering (GISAXS) patterns displayed in our original paper were actually reversed along the 2θf axis. Accordingly, the low-intensity streak corresponding to the steeper slope of the ripples should be located on the positive 2θf side in our original Figs. 6(a) and 7(a). This does not affect our methodology, and our quantitative results remain valid, except that the asymmetry factor A of the ripples is negative (and not positive as reported in our original Table I). The correct representation of the ripple shape is displayed in Fig. 1(a) of this Erratum where it appears that the as-etched Al2O3 and Si3N4 surfaces present a uniform pattern of asymmetric ripples with γ+ < γ− so that the side facing the ion beam is steeper than the opposite side. It is worth noting that both positive1–4 and negative5–7 values of A have been reported in the literature. Moreover, taking into account the correct negative sign for δy in Fig. 1(b) (i.e., in the Al2O3/Ag/Al2O3 trilayers, the surface roughness of the capping layer replicates the buried ripple pattern with an out-of-phase modulation), we have recalculated the 2D GISAXS patterns presented in our original Figs. 11(c) and 12(c). The corrected results are displayed in Figs. 2(c) and 2(d) of this Erratum, which show a better agreement with the experimental data [Figs. 2(a) and 2(b)] than in the original paper when assuming that the surface roughness of the capping layer replicated the buried ripple pattern with an in-phase modulation. It should be noted that the simulations presented in our original Figs. 11(d) and 12(d) are not affected by the sign of δy, and thus, they remain valid.

Preparation of gold nanoparticles for plasmonic applications

We present a simple hot injection method for the preparation of colloidal solutions of hydrophobic spherical gold nanoparticles with the diameter around 20nm and size dispersion below 20%. Various surfactants with different lengths of hydrocarbon chains, such as oleylamine, 1-octadecanethiol, poly (N-vinylpyrrolidone), and AgNO3 in 1,5-pentanediol, were used for sterical stabilization in the colloidal solution. The hydrodynamic nanoparticle size and size dispersion were determined by the dynamic light scattering (DLS) while the small-angle X-ray scattering (SAXS) from the colloidal solution provided information on the size of the metallic nanoparticle core (without surfactant). Plasmon enhanced resonant absorption peaks between 500nm and 600nm were detected by the UV–VIS spectrophotometry. The nanoparticle arrays on silicon prepared by solvent evaporation or Langmuir-Schaefer method were inspected by high-resolution scanning electron microscopy and grazing-incidence SAXS (GISAXS). The presence of side maxima in the GISAXS pattern gives evidence of the nanoparticle ordering by self-assembly while very close values of the interparticle distance derived from GISAXS and the nanoparticle size derived from DLS indicate a close-packed order.

Silicon Nanocrystal Superlattices

Silicon Nanocrystal Superlattices

Correlation between structure and optoelectronic properties in a two‐dimensional nanoparticle assembly

AbstractThe optical properties of two‐dimensional assemblies of metal nanoparticles are strongly influenced by the morphological configuration of the metal particles in the layer. Therefore, we correlate the structural and optical properties of two‐dimensional, hexagonal gold nanoparticle arrays. We characterize the structure of the arrays using grazing‐incidence small angle X‐ray scattering (GISAXS). From the GISAXS pattern, we determine the size of the gold particles as well as the lattice spacing of the hexagonal assembly. Based upon these parameters we calculate the dielectric function of the gold particle array using the Maxwell–Garnett effective medium theory. We further deduce the absorption spectrum which closely follows the measured absorption and photoconductance spectrum. (© 2011 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

A GISAXS study of the angular dependence of carbon nanotubes grown on a plain substrate by the dc HF CCVD process

We report on a quantitative Grazing Incidence Small Angle X-ray Scattering (GISAXS) study of the angular dependence of oriented carbon nanotubes (CNTs) grown by a catalytically activated, plasma direct current or plasma enhanced and hot filaments-assisted catalytic chemical vapour deposition (dc HF CCVD or PE HF CCVD) process. To synthesize these CNTs, some transition metal (TM) particles were used as a catalyst and dispersed on plain SiO2 (thickness 5 nm)/Si(100) substrates prior to the growth of CNTs. Some morphological (diameter, height) and disorder parameters have been determined using the GISAXS technique in the framework of Effective Layer Born Approximation (ELBA) and Distorted-Wave Born Approximation (DWBA) on noncorrelated multilayer systems. The GISAXS patterns, although dominated by envelope features of disordered islands, provide important complementary quantitative information about CNT films. The results are compared to scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations. Furthermore, the GISAXS patterns could only be acceptably reproduced by considering an inter-mixing C–Co contribution and the metallic cobalt let on top of the CNT. While monitoring the incidence angle, we found that the disorder parameter decreases with increasing incidence angle, showing that the in-plane system order increases from the surface to the inner layers.

On the intersection of grating truncation rods with the Ewald sphere studied by grazing-incidence small-angle X-ray scattering

In this work a grating made of lines having a height of 55 nm and a period of 450 nm has been characterized by grazing-incidence small-angle X-ray scattering (GISAXS). The GISAXS patterns are characterized by a series of spots corresponding to the intersection of the Ewald sphere with the grating truncation rods (GTRs). When the grating lines are almost parallel to the direct beam, the location of these spots is very sensitive to any change in the azimuthal angle. The precise location of the intersection of the GTRs with the Ewald sphere can be calculated for any azimuthal angle. From this analysis we can estimate the statistical coverage of the grating, its period and the width of the lines. In addition, the anisotropy of the width of the spots in theqzdirection is interpreted in terms of wavelength spread and angular divergence of the incident beam.

Stacking of Main Chain-Crown Ether Polymers in Thin Films

Thin films (9-70 nm) of a series of polymers containing in the main chain dibenzo-18-crown-6 ether unit (DB18C6) linked to an aliphatic spacer of different length (10C and 14C) and nature have been prepared, from chloroform solutions, by spin coating on a silicon substrate. The quality and homogeneity of the polymer coatings was revealed by their reflectivity spectra and atomic force microscopy (AFM). The grazing incidence small-angle X-ray scattering (GISAXS) patterns show an out-of-plane structure correlation (interference maximum near the horizon) of scale size related to the polymer repeating unit length. Above this Bragg reflection, the shape of the scattering observed, in the GISAXS pattern, reveals an orientation of the stacked molecular columns in the coated polymer. A thermal treatment of the samples improves the nanostructure by increasing the lamellar coherence size (in y-direction) as well as the vertical orientation of the molecular columns.